1. Field of the Invention
The present invention relates to a polishing pad and fabricating method thereof, and more particularly to a polishing pad and fabricating method of the same suitable to prevent particles from being generated during a polishing process.
2. Description of the Related Art
Nowadays, chemical mechanical polishing (CMP) processes are commonly used to achieve global planarization. In a conventional CMP process, polishing slurry containing abrasive particles is applied on the surface of a wafer and set in relative motion with respect to a polishing pad with appropriate elasticity and hardness for the purpose of planarization of the wafer.
FIG. 1 shows a top view and a side view of a wafer carrier holding a wafer on a polishing pad in a conventional polishing process. As shown in FIG. 1, a wafer 100 is held by a wafer carrier 102, for example, in a way that a retaining ring 104 is used to attach the wafer 100 on the bottom surface of the wafer carrier 102. The wafer carrier 102 holds the wafer 100 to spin on the polishing pad 110, and the polishing pad 110 itself also rotates driven by a polishing table, while a polishing slurry is provided between the surface of the wafer 100 and the polishing pad 110 for the polishing process. Abrasive particles in the slurry contact with and rub against the surface of the wafer 100, which causes abrasion on the surface of the wafer 100 and thus make the surface becoming planar. The relative motion between the polishing pad 110 and the surface of the wafer 100 includes not only rotational motion of the wafer 100 and the polishing pad 110 but also horizontal swing motion of the wafer 100.
Referring further to FIG. 1, when the wafer carrier 102 brings the wafer 100 slightly in a horizontal swing motion within the polishing region 112 of the polishing pad 110, the motion will induce a compressive stress on the polishing pad 110 towards the center of the polishing pad 110 so as to compress the central region 114 to become protruded. When the wafer 100 continues to be polished on the protruded polishing pad 110, the retaining ring 104 on the wafer carrier 102 may rub against the protruded surface of the central region 114 of the polishing pad 110 and thus generate particles. Since a trench 106 is ordinarily designed in the retaining ring 104 on the wafer carrier, the particles generated due to the rubbing may pass through the trench 106 in the retaining ring 104, reach the wafer 100, and further contaminate the wafer 100.
In addition, since the polishing surface of the polishing pad 110 is perpendicular with the sidewall 116 of the polishing pad 110, when the wafer carrier 102 brings the wafer 100 slightly in a horizontal swing motion within the polishing region 112, the retaining ring 104 on the wafer-holding device 102 may rub against the sidewall 116 of the polishing pad 110 to generate small particles, and the particles may pass through the trench 106 in the retaining ring 104, reach the wafer 100, and further contaminate the wafer 100.
During a conventional polishing process, as described above, the surface of the central region or the edge portions of the polishing pad may rub against the retaining ring of the wafer carrier, which will generates small particles to contaminate the wafer.